Anything I could think of would be heavily inspired by Master of Orion, so just look at this: http://www.gamefaqs.com/pc/197873-master-of-orion-ii-battle-at-antares/faqs/14668, and Ctrl+F to "random events list" for some inspiration. I particularly liked the space dragon who would show up and threaten to attack you unless you paid it (and would then let you direct it to another player's system if you could cough up the dough).